The electrocatalytic hydrogen evolution reaction in the presence of a metal-free organic catalyst based on 1,10-phenanthroline: the first example of a reaction proceeding by an intramolecular mechanism

Abstract

This article presents data on the electrocatalytic activity of new members of the metal-free electrocatalyst family, 1,10-phenathroline and N-methyl-1,10-phenathrolium iodide, for the hydrogen evolution reaction (HER) in the presence of perchloric acid (HClO₄) and trifluoroacetic acid (CF₃COOH). It has been shown that the efficiency and mechanism of the electrocatalytic process strongly depend on the nature of the catalyst and the pK_a value of the acids. In the presence of HClO₄ and 1,10-phenathroline, the cyclic voltammogram shows the appearance of two electrocatalytic waves, while in the case of N-methyl-1,10-phenathrolium iodide, only one wave is observed. In the presence of CF₃COOH, only one electrocatalytic wave is observed for 1,10-phenathroline and no such waves are formed for the N-substituted salt. For the first time, the possibility of the HER occurring at different potentials, according to the same mechanism, has been shown: in the case of 1,10-phenathroline and perchloric acid, the hydrogen evolution reaction at potentials of E = −0.6 V and E = −0.25 V proceeds through the same key intermediates. Using the DFT method, the mechanisms of the occurring processes were studied, and key intermediates were identified.